Autism spectrum disorders (ASD) are defined, in part, by behavior that can be characterized as restricted and inflexible. Such behavior is exemplified by the so-called higher order restricted repetitive behaviors characterized by their insistence on sameness or resistance to change. Behaviors characterized in this way are pervasive in children with ASD and can significantly interfere with opportunities to develop functional behaviors and more complex repertoires. Thus, restricted, inflexible behavior likely adversely impacts brain and behavioral development, and intervention directed toward such behavior should have significant positive impact on neuroplasticity and neurodevelopmental trajectories. The overall goal of the proposed project is to initiate a program of research to develop a novel treatment approach to restricted, inflexible behavior, a clinically important and highly understudied problem in neurodevelopmental disorders in general and autism in specific. Rather than target a particular compulsive, restricted, or repetitive behavior for modification, our proposed strategy is to promote the development of flexibility and variability using age appropriate, functional activities. As such, the proposed project is highly translational as our approach to intervention is based on a body of animal and human laboratory studies that have established the empirical foundation for such an approach. Effective interventions are hypothesized to have generalizable effects on development and will be highly translatable to other neurodevelopmental disorders. Thus, we propose to assess restricted, inflexible behavior in children with ASD and typically developing controls and then pilot test an experiential intervention to determine if it will directly promote variable and flexible adaptive responding in children with ASD. This project is highly innovative in targeting flexibility and variability as goals of the intervention. No systematic efforts have been made to develop effective methods for the behavioral treatment of the general rigidity/inflexibility that is most characteristic of autism and common in related neurodevelopmental disorders. Finally, the proposed project represents a translational effort to take laboratory-based animal and human studies and apply them to a focused intervention directed at restricted, inflexible behavior that can ultimately be conducted in a community setting. If successful, the proposed treatment approach should have considerable potential for becoming a widely used, cost effective treatment approach.